AimTo reach a consensus on question items for early identification of unmet psychosocial needs of school‐aged siblings of children with cancer and blood disease.DesignModified Delphi method.MethodsTwenty‐three studies were reviewed to extract question items, which were classified into seven categories. A total of 39 question items were selected for this study. The selected question items were carefully considered using the modified Delphi method. The participants were 28 medical staff from a childhood cancer hub hospital and 20 sibling support group staff members. The first round consisted of a questionnaire (n = 48); the second, a focus group interview (n = 8) and the third, another questionnaire (n = 8). The first and third rounds used a 5‐point Likert scale. This survey was conducted from July to October 2021.ResultsA total of 38, 26, and 24 question items were included in the first, second, and third rounds respectively. A total of 24 question items were extracted using the modified Delphi method to identify siblings' unmet psychosocial needs: relationship with family members, 3; daily life issues, 4; stress, 6; emotions, 3; information, 3; relationships with medical staff, 1 and social and medical resources, 4. Seven categories and 24 question items were confirmed as items for identifying the unmet psychosocial needs of school‐aged siblings of children with cancer and blood disease.